AI Summary
5 min readThe Case Against Pluto’s Planethood—and What’s Hiding Beyond It
In this grab-bag edition of StarTalk Cosmic Queries, Neil deGrasse Tyson fields questions ranging from the possibility of a ninth planet lurking beyond Neptune to why Pluto got demoted, how galaxies get their shapes, and whether dark matter could be ordinary matter folded into the fabric of spacetime. The episode’s most sustained and substantive thread concerns the evidence for Planet Nine and the logic behind Pluto’s reclassification—two topics that together illuminate how science revises its categories when new data forces the issue.
The Evidence for a Hidden Planet
A listener from Thousand Oaks, California, asked what observations are causing astronomers to suspect a large planet or dwarf planet exists far beyond Pluto—sometimes called Planet X or Planet Nine. Tyson explains that the case rests on the behavior of Kuiper Belt objects, the icy bodies orbiting in the region beyond Neptune that includes Pluto itself. These objects show orbital anomalies that cannot be fully explained by the Sun’s gravity alone. Something else is tugging on them.
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What you'll learn
- 1 Cosmic Queries – Planet 9
- 2 (03:32) **Andy L's Question: What's the Evidence for Planet 9?** - Listener asks about the scientific observations causing suspicion of a large planet beyond Pluto, and whether the Rubin telescope could find it.
- 3 (08:48) **Eric LaRoy's Question: Why Was Pluto Demoted?** - Listener argues the IAU's "clearing its neighborhood" criterion is too vague and suggests reinstating Pluto would boost scientific interest.
- 4 (17:17) **Pluto's Unlikely Legacy: The Element Plutonium** - Neil notes that plutonium, element 94, was named after Pluto while it still had planetary status—making it "the most destructive non-planet ever."
- 5 (22:10) **Narab Shah's Question: Relativity, Quantum Physics, and Semiconductors** - Listener asks for the connection between relativity, quantum physics, and semiconductor physics.
- 6 (25:45) **Derek Evans's Question: What Dictates a Galaxy's Shape?** - Listener asks what determines galaxy shapes, whether they all rotate, and if shape indicates age or developmental stage.
- 7 (30:10) **Peculiar Galaxies and Collision Simulations** - Neil describes how computer simulations in the 1970s finally explained the "peculiar" galaxies in Halton Arp's catalog.
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Guests on this episode
Show Notes
Could there be a hidden planet lurking beyond Pluto and Neptune? Neil deGrasse Tyson and comic co-host Chuck Nice tackle a wide-ranging grab bag of fan questions covering Planet 9, galaxy shapes, dark matter, the odds of getting hit by a meteorite, and more!
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Thanks to our Patrons Glenn Fiskin, A. Certain Woman, Jeffrey Schwartz, Adam Watson, Micheal Lawson, Aaron Hardy, Terje Berg, Peter Wells, Tyler, Brody Johnson, Ali, NanZan, SAMuri, Marian Bieniek, Jeff Whitney, Richard Ruffner, Adrian J Batson, Holly Grant, Amy Braden, Andrew Puente, Srihari Ravi, Eliezar Vega, Southern Tauren, Adam Tate, John Johnson, Achim Ferrandina, Rebecca Crowe, Cody May, Gary, William Green, Max_Palmer09, Dylan, Jonas and Aisté, Frank Pucino, Isaac Kinsey, Sean Whitehall, Anthony Prisco, Nathan Thornton, Alex Grzesiak, Lora Vatalaro, Manny Neto, Eric M, Robert Davies, Billy Metcalfe, Gabriel Gish, Sherry Lee Rachar, Alexander Nemeth, Ra.Spec, and Atticus Thompson for supporting us this week.
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